This application claims priority to and the benefit of U.S. Provisional Application No. 60/631,895, filed Nov. 30, 2004, which application is incorporated herein by reference in its entirety.
The present disclosure relates to a method of isolating a control signal from a power line using a charge pump circuit. It finds particular application in conjunction with ballast controlled gas discharge lamps and discrete dimming systems and will be described with particular reference thereto. However, it is to be appreciated that the exemplary embodiments of this disclosure are also amenable to other like applications.
Many types of dimming ballasts have been proposed that control the arc current of a gas discharge lamp such as a fluorescent lamp. One type includes an external means of heating the cathode to prevent sputtering of the cathodes whenever the arc current is reduced to less than 50% of its rated value. The efficiency of such a dimming circuit falls off as the light intensity is reduced.
Multiple ballast dimming systems control fluorescent lamps either in pairs or individually. For example, a three lamp fixture may have a two lamp ballast and one lamp ballast whereby the light intensity can be changed from 33% to 100% of its rated value by turning on a specific ballast. This requires at least two ballasts to cover a 3 to 1 range in brightness, which may increase cost and impact the available space in the fixture. Also, a latching relay is used to turn the ballasts on and off which requires a power supply to activate the relay coil.
Dimming systems capable of operation, as described above, are further described in U.S. Pat. No. 6,686,705, issued to Nerone et al., and “A Discrete Dimming Ballast for Linear Fluorescent Lamps”, authored by Haiyan Wang, and these references are hereby totally incorporated by reference.
A better system capable of powering a plurality of lamps is desirable from an efficiency perspective and from a packaging and cost perspective. In addition, it is desirable to have a circuit to isolate a low voltage control signal used for activating discrete dimming levels without using external power supplies from the power line voltage, the low voltage control signal selecting individual lamps for a discrete dimming system.